ANPEP and neoplasm: Another hormone-regulated protein identified in this study is aminopeptidase N (APN/CD13), a transmembrane Zn2+-dependent ectopeptidase that cleaves N-terminal neutral amino acids of various peptides and proteins, and is implicated in various processes, including cell proliferation, tumor invasion and angiogenesis [31], [32], with high expression correlating with malignancy [33].